TRUE DRY ROT – The Facts
Our inspection revealed an infection by true dry rot (TDR) which is the every day name given to the wood rotting fungus serpula lacrymans.
The reasons for TDR having developed within your property can not be stated with complete certainty but generally speaking, it will develop as a result of moisture having entered the structure as a result of external defects or, in some cases, due to plumbing leaks and it may be that our surveyor has been unable to determine the original likely cause for the development of the fungal attack.
One of the main characteristics of TDR is that it is able to transfer moisture from wet areas via its hyphae (root like structure), to areas which were unaffected by the original water ingress. This is why it is called dry rot because it is able to feed on timbers that have no direct moisture source other than that being conveyed by the fungal infection itself.
Once established, TDR can spread rapidly with growths of up to 1 metre per month being recorded. Severe damage is caused to timber by the ‘mycelium’ (this is secondary growth of a substance which is ‘cotton wool’ like in appearance) and produces an enzyme which is highly corrosive to timber causing it to breakdown rapidly, giving access to the cellulose within the timber that the dry rot is feeding on. Timber affected by TDR can be structurally weakened very quickly. The timber will appear to shrink and most often is affected by what is known as cuboidal cracking, which means that the timber breaks both along and at right angles to the natural grain. Timber that bears dry rot infection can never be treated as the destructive elements of the fungal attack can be deep inside the timber itself. The only solution is to cut back the infected timber to a minimum distance of up to 1 metre beyond the last visible signs of the fungal attack whilst regularly inspecting the cut end to ensure the cut grain appears completely clean and free from any staining which might be as a result of the infection itself.
One of the major problems with TDR is that it often grows unseen behind plaster, wall linings and ceilings. It is difficult to eradicate without fully exposing the infection itself, and this means that internal wall plaster etc., will need to be removed to a distance of up to 1 metre from the last visible signs of the root complex. It is not uncommon for a small area of TDR to be identified on a skirting board or perhaps around a doorframe etc., where the impact on the timbers appears quite small but on removal of plaster the spread of the fungal attack can extend to many metres and it can be feeding on hidden timbers embedded within the walls such as lintels and joist ends both above and below. To risk leaving any active infection within the building is highly likely to lead to new outbreaks in the future and this is the reason why it is sometimes necessary to remove large areas of plaster to be absolutely certain that the preparatory work has extended far enough to ensure that it is totally eradicated.
Sometimes it is possible for our surveyors to accurately identify an area of infection and give a fixed price quotation but on other occasions, even with our own technicians carrying out the preparatory work, our surveyor will want to re-visit and evaluate the situation when all exposure is completed. It may be that the price that we will quote you for the sterilisation work will have a guide cost rather than being a fixed price quotation to allow for the problems that might be discovered later. Some companies deal with this in a different way and it may be that a quotation received from a competitor will seem at first glance to be cheaper. If this is the case we would strongly advise you to look at their small print as no matter how good the surveyor is, it is often impossible to be absolutely certain as to how far the problem extends until that exposure work is complete.
In cases where the customer chooses to employ a separate contractor to carry out the preparation we must make you aware of the pitfalls that exists. If we are carrying out the preparation, our expertly trained technicians know what they are looking for and will try to identify the extent of the infection by removal of small areas of plaster first so as not to disturb the evidence that they are looking for during the course of that preparation work. Somebody not as well-versed in the habits of TDR may take a totally different approach and believing they have got to the end of an area of infection, may decide they have gone far enough because they have actually destroyed that important evidence too early. For this reason alone, if you decide not to employ us to carry out the preparatory works then the guarantee that we will eventually give will be confined solely to the area that we have treated and not cover adjacent areas unless it is our own technicians that have carried out that preparation. If the preparation is carried out by somebody else, then we would never be in the situation of being able to see the evidence of the attack because at that stage it is likely to have been removed when the exposure work was carried out by the other contractor. It will be our aim, if we are carrying out that work, to restrict the removal of plaster etc., only to the area that is necessary to be treated and this could represent large savings in cost as well as giving you the peace of mind of knowing that everything is covered by guarantee.
There are a number of other golden rules that must be followed and they are as follows:-
Quite literally every scrap of old timber within the area of infection must be removed and all timber being discarded should be removed from the site and if possible burnt. When replacing timber such as joist ends, lintels and other structural timbers that might come into contact with damp masonry, these new timbers must be isolated by the use of physical membranes. New or replacement timbers must never be allowed to come into contact with masonry in any property that has ever suffered from TDR and in any case this is considered to be bad practice. Where timber wallplates existed, they would normally be removed and replaced with non-organic materials such as concrete and where possible damp proof membranes installed to ensure that where the timbers bear upon them, the masonry is completely dry.
When dealing with infections at ground floor level where timber suspended floors exist and prior to installing either a new timber floor or replacing it with a concrete floor, it is imperative that the sub-site is scrupulously cleaned of all organic debris, including even the smallest scraps of timber. Infected timber left beneath a floor could give rise to a new infection, even after treatment.
Generally speaking, the use of timber for the replacement of lintels and structural beams etc., should be avoided wherever possible and substituted with, for example, concrete lintels or steel beams. We can advise you on this should such be found necessary.
When replacing wall plaster in older style properties we would always advise that replastering is carried out in accordance with the separately enclosed replastering specification which is referred to again later in this report.
A few words about floors
Where timber suspended floors exist, these can be affected by TDR as a result of inadequate ventilation to the sub-floor area. Timbers of suspended floors without adequate ventilation can be subject to high moisture contents as a result of condensation and it is important if this situation exists to increase ventilation when possible. If adequate ventilation cannot be provided however due to extensions having been built and the close proximity of other buildings or structures, then it may be necessary to consider replacing the timber floor with a solid floor incorporating damp proof membranes, again our surveyors will advise on this item.
Where concrete floors already exist, problems of dry rot are often found affecting skirting boards and doorframes and this is normally an indication that the dry rot, having already developed, has been able to extend its root strands beneath the solid floor from where it is drawing and transferring moisture to areas that were previously dry. In this case it is sometimes necessary to remove all or sometimes sections only of the solid floor to enable sterilisation of the sub-site to take place, which will eradicate the root growth itself.
We must give one more word of warning, we have on numerous occasions, even after advising on TDR, found situations where clients have removed timber suspended floors and replaced them with concrete, thinking that by removing the food source i.e. the timber floor itself, this will eradicate the infection. In doing this the dry rot infection has been buried beneath the new solid floor and can quickly start to re-grow appearing later on skirting boards that were not even affected before. The only way to eradicate this type of attack is to completely remove the solid floor again to allow for deep sterilisation of the sub-site and we would caution you against the high risk of taking such an approach.
The treatment itself
Regardless of who has carried out the preparatory work, the sterilisation works that will be carried out by us will be as follows and treatment is always carried out prior to any reinstatement of timber and plaster etc.,
Our technicians will decide whether to use what is known as ‘toxic box’ treatment or ‘blanket’ treatment and this will depend on a number of factors including the size of the infection and taking into account difficulties that might exist relative to the number of rooms affected which may be broken up by internal dividing walls/ceilings separating various rooms or floors.
‘Toxic box’ treatment involves drilling a series of holes into the wall structure that will surround the area of infection and provide a barrier that prevents the infection from travelling past and into new areas of the property. These holes are high pressure injected with powerful fungicides that form a deep barrier within the masonry itself.
‘Blanket’ treatment is often used where the infection has spread in an irregular pattern and takes the form of ‘pepper pot’ drilling of entire wall surfaces to eradicate areas of deep seated fungi within the masonry by the pressure injection the fungicide into the many drilled holes. Sometimes both of these methods are used in combination where conditions dictate that this is necessary.
In addition to either of the above two methods, the surface of affected masonry and sub-floor areas will have similar fungicides applied on the surface and this will complete the sterilisation operation.
We fully understand that some clients are faced with this problem with no warning whatsoever and time is sometimes needed to gather the financial resources to tackle the problem. It is sometimes possible to ‘buy time’ and carry out a holding operation which will slow the attack down and if this is your situation please speak to one of our technical advisors who will sympathetically try to find a way to gain you some time. We will never offer you this however, unless there is no other option or if we think that a holding operation is inappropriate in your case.
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